Method for the preparation of lightsensitive diazotype materials and improved materials prepared by such method



United States Patent 3,353,984 METHOD FOR THE PREPARATION OF LIGHT- SENSITIVE DIAZOTYPE MATERIALS AND IM- PROVE!) MATERIALS PREPARED BY SUCH METHOD Raphael Landau, 9 Markhams Drive, Woodford Green, Essex, England No Drawing. Filed Apr. 15, 1964, Ser. No. 360,131 Claims priority, application Great Britain, Apr. 18, 1963, 15,269/63; May 24, 1963, 20,834/ 63 12 Claims. (Cl. 11734) This invention relates to an improved method for the preparation of light-sensitive diazotype materials and to improved light-sensitive diazotype materials prepared by such method.

Coating solutions or dispersions usually employed in the preparation of light-sensitive diazotype materials may comprise one or more light-sensitive diazonium compounds, one or more coupling components, a dye coupling inhibitor such as an acid, anti-yellowing compounds such as thiourea and humectants such as zinc chloride.

A method of preparing light-sensitive diazotype materials is already known in which a base material support such as, for instance a paper base material is first coated with a pre-coating composition and is subsequently coated with a sensitizing composition such as, for instance,

. of the kind referred above.

The pre-coating composition usually comprises a substance having a colloidal structure but it has not heretofore contained the essential element of the sensitizing composition, namely the diazo constituent.

Another known method of preparing light-sensitive diazo type materials is to coat the base material or support with a solution which contains both the sensitizing and the pre-coating ingredients.

In the first-mentioned known method two separate coating steps are required while in the latter only one coating step is necessary.

It is an object of the present invention to provide an improved method of preparing light-sensitive diazotype materials which permits the selection of a greater range of diazonium compounds and coupling components and which results in the production of diazotype materials of surprisingly increased sensitivity and/or density.

An improved method of preparing light-sensitive diazotype materials according to the present invention comprises coating a base material or support with two separate coating solutions or dispersions, a first solution or dispersion comprising a part or all of the diazonium compound or diazonium compounds comprising the sensitizing composition with or without a part of the other ingredients comprising said sensitizing composition, while the second solution or dispersion, which is applied to the base material or support subsequently to the application of said first solution or dispersion, contain the other ingredients comprising the sensitizing composition and the remaining part (if any) of the diazonium compound or diazonium compounds, said second solution or dispersion being so constituted as to prevent any substantial removal of the diazo from the first coating during application of said second coating.

The second solution or dispersion is applied to the same surface of the base material support either before or after the first coating is dried.

Where the second coating is applied before the first coating is completely dry a few seconds should be allowed for absorption of the superficial liquid, before the second coating is applied.

This method of procedure can be termed after-coat: ing to distinguish it from the term pre-coating where ice all the diazo compound is present in the second coating solution and it has the following advantages:

The method of the present invention permits the sensitization of the base material or support with sensitizing elements which it has not been possible to use heretofore as these would otherwise precipitate if included together in the same solution. This is the case with numerous diazos and couplers having excellent qualities for use in the preparation of diazotype materials but which, due to their incompatability in solution, it has not previously been possible heretofore to incorporate them in the same sensitizing solution.

Thus, the improved method of the present invention increases considerably and in an unexpected manner, the possible combinations of diazo and coupling components which can be employed in the preparation of lightsensitive diazotype materials.

In many cases the method of the present invention results in a surprising increase in sensitivity and/0r density. This is possibly due to the fact that when paper, for instance, is sensitised with a highly concentrated solution only part of the products is absorbed into the base while much is precipitated over the fibres of the paper. This precipitation is due to the high concentration of the sensitising solution augmented in part by a partial evaporation of the solvent during drying and in part by the selective solubility of the solvent in the support. The precipitated products are unable to penetrate into the interior of the fibres. It is known that precipitated diazos in a weakly or non-ionized form are less sensitive to light.

It is probable, therefore, that the usual pre-coat prevents precipitation of the diazo in a weakly or non-ionized form which remains on the exterior of the fibres. This explanation would account for the increased sensitivity of ordinary pre-coated materials.

With the method of the present invention it is possible to produce the first solution or dispersion in such a way that all the diazo is in an ionized and well dispersed form.

This explanation is given only to facilitate an understanding of the invention but it is not intended to limit the invention in any way.

The second solution or dispersion which may be termed the overcoatmay contain precipitants and is preferably such as not to wash out the diazo applied to the base by the first coating although small quantities of diazo which may be deposited. on the surface of the base fibres may be removed by washing without deleterious effects.

Where the diazonium compound or diazonium compounds of the first coating solution or dispersion is, or are, relatively soluble the action of the precipitant should be correspondingly vigorous. In general, the more soluble the diazo or diazos, the more vigorous should be the action of the precipitant.

The second coating solution should not contain substances which would dissolve any substantial amount of the diazo already deposited by the first coating.

Thus the second coating solution should contain agents which reduce the solubility of the diazo, for example, substances which form sparingly soluble double salts with the diazo, such as zinc chloride, stannous chloride,

cadmium chloride, the tungstates, the fluoroborates, the

silicofiuorates, the chlorates and sulphates of alkaline or alkaline earth metals, sulphonated or non-sulphonated couplers, soluble ferrocyanides such as alkaline metal fer-rocyanides, sulphonated benzene or naphthalene and in general any substances which diminish the solubility of the diazo without decreasing its sensitivity, may be employed.

It is also preferable to add to the second solution substances which are easily soluble in water or in the solvent I employed. It may sometimes be useful to add small proportions of soluble substances to the first coating solution. This procedure may be useful, for instance, when soluble acids which protect the diazo against decomposition on drying are employed.

These substances will be partially re-dissolved by the second solution but as they are used in small quantities they will only modify the second coating slightly. This slight modification of the composition can be easily compensated by a feeder modification to the second bath.

The second coating solution may contain diazo compounds which may be different from those used in the first coating solution. They should not, however, precipitate with the products used in the second coating which are used to insolubilise the diazo in the first coating, or used in an amount below the precipitating concentration.

The first and second coating solutions may contain constituents usually employed in the heretofore known precoating composition, for instance, silica or other pigments, binders such as starch, polyvinyl acetate, polyvinyl-alcohol, gelatine and other colloids.

The method of the present invention has a further advantage in that prints produced from the materials prepared thereby have less tendency to bleed than when coated by known methods.

This is due to the fact that diazos yielding insoluble dyes can be used which would otherwise be incompatible With the coupler if used in the same solution.

A further advantage of the method of this invention resides in the increase of the brightness of the dye formed due probably to the fact that the dye formed is in a more divided state on the surface.

The method of this invention may be applied to all processes such as the one or two-component processes for semi-dry or ammonia gas development respectively or for heat development processes or similar processes.

All diazos soluble in water can be used for the purpose of sensitising a support which absorbs or is swollen by water. All diazos soluble in a mixture of water and organic solvent or in an organic solvent or a mixture of organic solvents without water can be used when the supports absorb or are swollen by these solvents. The diazo can also be dissolved in a colloid which is deposited on the base and in this case the colloid constitutes the carr er.

One such diazonium compound which is known to possess certain excellent characteristics, is 2,5 di nbutoxy-4-morpholino benzene diazonium chloride, which has previously rarely, if ever, been employed, in the preparation of two component light-sensitive diazotype ma-' terials, due to the fact that it precipitates when in solution with practically all couplers. Its solubility in water is limited but it is high enough to give on printing strong line density; on the other hand, it is not soluble enough to be washed out by the overcoat containing the precipitant.

Thus, an improved method of preparing two component light-sensitive diazotype materials according to the present invention, therefore, comprises coating a base material or support with a first solution or dispersion comprising 2,5 di-n-butoxy-4-morpholino benzene diazonium chloride, together with certain of the other ingredients of the sensitising composition, but not including the coupling component and then before or after the first coating is dry with a second solution or dispersion comprising 2,3-dihydroxy naphthalene together with the remaining ingredients of the sensitising composition.

An improved two component light-sensitive diazotype material according to the present invention comprises a base material or support coated with a first solution or dispersion comprising water, 2,5.di-.n-butoxy-4-morpholino benzene, diazonium chloride, citric acid, silica and polyvinyl acetate aqueous dispersion and then with a second solution or dispersion comprising water, 2,3-dihydroxy naphthalene, citric acid, zinc chloride, sodium thiocyanate, thiourea and diethyle e, glycol.

Any other suitable light-sensitive diazonium compounds may be employed, the following being included as examples:

Coupling components soluble in water can be used in the sensitisation of supports which absorb or are swollen by water. Coupling components soluble in a mixture of water and organic solvents or in a mixture of organic solvents without water can be used to sensitise supports which absorb or are swollen by these mixtures.

Any suitable coupling components may be used in the method of the present invention, the following being examples:

(a) Phenols and substituted phenols e.g. p-xylenol (b) Polyhydroxyphenyls and substituted polyhydroxyphenyls e.g. resorcinol, octyl-resorcinol, phloroglucinol, resorcylamines (c) Naphthols and substituted naphthols:

2,3-dihydroxy naphthalene-S-sulphonic acid 2-hydroxy naphthalene-6-sulphonic acid Beta hydroxynaphthalene amides (d) Couplers containing a reactive methylene groups:

1-phenyl-3-methylpyrazol-S-one. Acetoacetanilides.

The. following stabilising components can be used:

Thiourea;

Naphthalene sulphonic acids;

Organic acids such as citric acid or tartaric acid and inorganic acids such as sulphuric acid or hydrochloric acid;

Salts of inorganic acids such as zinc chloride and aluminium sulfate, cadmium sulphide, magnesium chloride etc.

The .following hygroscopic agents and development accelerators such as for example, polyglycols, glycerol, 1- allyl-3-[3-hydroxyethyl-2-thiourea may be employed.

A particularly useful and important feature of the present invention is that it is possible to include in the second coating solution or dispersion of a soluble thiocyanate salt and/ or zinc chloride, to act as a precipitant.

Paper, tracing cloth, saponified or non-saponified cellulose acetate films, films of polyethylene, polyamide, polystyrene and other plastic materials, metal foils particularly aluminium foils having a layer of aluminium hydroxide thereon can be employed.

The present invention is illustrated by the following examples:

EXAMPLE 1 A paper base material is coated first with the following solution:

Bath N0. 1

mls. water 2.5 grammes colloidal silica and 5 mls. of a 50% poly-- vinyl acetate emulsion can be added to this bath After drying the folowing solution is applied to the same surface:

Bath No. 2

Water mls 100 2,3-dihydroxynaphthalene-6-sulphonic acid (sodium salt) grammes 3.5 Thiourea do Zinc chloride do 6.5 Sodium sulphoscyanate do 1 Polyglycol do 3 Citric acid do 5 Aluminium sulphate 'do .5

This material after exposure and development by ammonia gas gives intense blue copies of improved contrast which are water fast and with a white background, If a pencil original is used for the exposure, the resulting print has a very uniform background.

If the constituents of the two baths above mentioned are combined into one bath considerable crystallisation which eliminates 80% or more of the diazo in the formula results.

If one both only with the constituents of the second bath added to it were employed by adding to it a diazonium compound more soluble than the one of the first bath for example p-diazodihydroxy ethylamino aniline a material is obtained 20 to 30% less sensitive with less contrast and paler lines with a very grainy background and on which the lines would run on moistening.

EXAMPLE 2 The procedure of Example 1 is followed but the two boths have the following different constituents:

A material is obtained having a dense black line with excellent stability, contrast, uniformity of background and fast to water. The elements of the two baths cannot be combined into one bath without crystallisation occurring.

EXAMPLE 3 A paper base material is sensitised with the following two baths to obtain a material suitable for semi-dry development:

Bath N0. 1

Water mls 100 2,5-dibutoxy 4 benzoylamino benzene diazonium chloride zinc chloride grammes 2 Citric acid do .5

Silica do 2.3 50% P.V.A. emulsion mls 4 The coating after doctoring is allowed to penetrate for a few seconds and is then overcoated without further drying with the following bath:

6 Bath N0. 2

Water mls 100 Rice starch grammes 0 Sodium chloride do 6 Zinc chloride d0 1 Thiourea d 1 Sodium thiocyanate d0 1 Citric acid do---- 15 The rice starch constituent is optional.

The following developing bath is employed:

Water mls 100 Potassium borate grammes 4 Phloroglucinol do 0.6 Resorcinol do 0.4 Potassium carbonate do 1 Wetting agent do .1

A material is produced having a blacker line and a sensitivity 30% greater than if the solution of Bath No. 1 were employed with three times the quantity of citric acid which is the usual sensiti-sing solution and no second bath were used. On the other hand, the addition of the elements of the second bath to the first would result in crystallisation.

If the diazo of Bath No. l is replaced by the diazonium salt of p-ethyl benzylamino aniline the increase of sensitivity would be still greater, of the order of 40%.

EXAMPLE 4 Tracing paper is sensitized successively with intermediate drying with the following baths:

Bath N0. 1

Water mls 70 Ethyl alcohol mls 30 Dibutoxy 4 morpholino: 1 diazonium benzene diazonium chloride grammes 2.5

Citric acid do .5

Bath N0. 2

Water mls Ethyl alcohol mls l5 Citric acid grammes 2 Thiourea do 3.5 Zinc chloride d0 8 Sodium sulphocyanate do 1 Mannich base of xylenol do 3 R salt do .7

A transparency is obtained for intermediate copies which ,is extremely sensitive and durable giving yellow brown lines.

EXAMPLE 5 A non-saponified cellulose acetate film suitable for diazo-type material is sensitised with intermediate drying with the following baths:

Bath N0. 1

Water mls 50 Methyl alcohol mls 50 Para-dimethylamino benzene diazonium chloride borofiuoride grammes 5 Concentrated phosphoric acid mls .3

Bath No. 2

Water mls 50 Methyl alcohol mls 50 Concentrated phosphoric acid mls 2 Thiourea grammes 2 Zinc chloride do 1.5 Ammonium sulphocyanate do 1.0 Resorcinol do 2.8 Phloroglucinol do .5

A film thus sensitised produces intermediate copies of high quality.

A two component light-sensitive diazotype material comprises a base material or support coated with a firstsolution or dispersion, prepared as follows:

Water mls 100 2,5-di-butoxy-4-morpholino benzene diazonium chloride grammes 1 Citric acid do 0.5 Silica ..do 5 50% polyvinyl acetate aqueous dispersion mls 5 and with a second solution or dispersion prepared as follows:

In general it has been found that by increasing the zinc chloride content the brightness of the print colour also increases and the shelf-life of the material is enhanced.

It will be noted that the second coating solution or dispersion includes sodium thiocyanate which, as previ ously mentioned, has been found to be particularly satisfactory as a precipitant. Alternative thiocyanates may include ammonium thiocyanate, zinc thiocyanate or indeed any other thiocyanate soluble in the solvent of the second coating solution or dispersion.

What I claim as my invention and desire to secure by Letters Patent is:

1. A method of preparing a light-sensitive diazo-type material which method comprises applying to a base material a first solution or dispersion containing a diazonium compound to form a.first coating and subsequently applying directly over the said first coating a second solution or dispersion containing a diazonium compound and a precipitant for the diazonium compound to form a second coating, the said second coating being contiguous with the first coating, said precipitant being selected from the group consisting of thiocyanates, tungstates, fluoroborates, silicofluorates, chlorides and sufates of the alkaline or alkaline earth metals, water soluble ferrocyanides and sulphonated benzene or naphthalene.

2. The method according to claim 1 wherein the precipitant is a thiocyanate.

3; The method according to claim 1 wherein the precipitant is a silicofluorate.

4. The method according to. claim 1 wherein the precipitant is a water soluble ferrocyanide.

5. The method according to claim 1 wherein the precipitant is a sulphonated benzene.

6. A method of preparing light sensitive diazotype materials according to claim 1 wherein the second coating solution or dispersion is applied either before or after the first coating solution or dispersion which has been applied to the base material is dried.

7. A method according to claim 1 wherein the second coating solution or dispersion contains a diazonium compound difr'erent from that contained in the first coating solution or dispersion.

8. A method according to claim 1 wherein the diazonium compound in the first solution or dispersion is 2,5-di-n-butoXy-4-morpholino benzene diazonium chloride.

9. A method according to claim 1 wherein the second solution or dispersion contains 2,3-dihydroxy naphthalene.

10. A method according to claim 1 wherein the second solution or dispersion includes the di-ethanolarnide of betahydroxy-naphthoic acid.

11. A method according to claim 1 wherein the first solution or dispersion is an aqueous dispersion or solution containing citric acid, silica and polyvinyl acetate.

12. A method according to claim 1 wherein the second solution or dispersion is an aqueous solution containing 2,3-dihydroxy naphthalene, citric acid, sodium thiocyanate, thiourea and diethylene glycol.

References Cited UNITED STATES PATENTS 2,616,803 11/1952 Ravich 96-49 2,617,726 11/1952 Kessels 9691 X 2,659,672 11/1953 Leuch 9691 X 2,793,118 5/1957 Sanders et al. 96-91 3,028,240 4/ 1962 Werner et a1 96-91 3,046,128 7/1962 Klimkowski et al. 96-75 X 3,061,397 10/ 1962 Streck 844 X 3,102,812 9/1963 Welch 9675 3,113,023 12/1963 Mellan 96-49 X FOREIGN PATENTS 571,802 9/ 1945 Great Britain. 864,011 3/ 1961 Great Britain.

OTHER REFERENCES Diserens, L.: The Chemical Technology of Dyeing and Printing, vol. II, Reinhold Pub. Co., New York, 1951 (p. 237 relied on).

NORMAN G. TORCHIN, Primary Examiner.

C. L. BOWERS, 11s., Assistant Examiner. 

1. A METHOD OF PREPARING A LIGHT-SENSITIVE DIAZO-TYPE MATERIAL WHICH METHOD COMPRISES APPLYING TO A BASE MATERIAL A FIRST SOLUTION OR DISPERSION CONTAINING A DIAZONIUM COMPOUND TO FORM A FIRST COATING AND SUBSEQUENTLY APPLYING DIRECTLY OVER THE SAID FIRST COATING A SECOND SOLUTION OR DISPERSION CONTAINING A DIAZONIUM COMPOUND AND A PRECIPITANT FOR THE DIAZONIUM COMPOUND TO FORM A SECOND COATING, THE SAID SECOND COATING BEING CONTIGUOUS WITH THE FIRST COATING, SAID PRECIPITANT BEING SELECTED FROM THE GROUP CONSISTING OF THIOCYANATES, TUNGSTATES, FLUOROBORATES, SILICOFLUORATES, CHLORIDES AND SUFATES OF THE ALKALINE OR ALKALINE EARTH METALS, WATER SOLUBLE FERROCYANIDES AND SULPHONATED BENZENE OR NAPHTHALENE. 